Motorola Gm328 Gm338 Gm398 Detailed 6804112j18 E Manual

							Frequency Synthesis2-9
The external RX buffers (Q5332) are enabled by a high at U5201, pin 3 (AUX4) via transistor switch 
Q5333. In TX mode, the modulation signal (VCOMOD) from the LVFRAC-N synthesizer IC (U5201, 
pin 41) is applied to the modulation circuits CR5321, R5321, R5322, and C5324. These modulate 
the TX VCO frequency via coupling capacitor C5321. Varactor CR5321 is biased for linearity from 
the VSF.
4.4 Synthesizer Operation
The synthesizer consists of a low voltage FRAC-N (LVFRACN) IC, reference oscillator (crystal 
oscillator with temperature compensation), charge pump circuits, loop filter circuits, and dc supply. 
The output signal (PRESC_OUT) of the VCOBIC (U5301, pin12) is fed to of U5201, pin 32 (PREIN) 
via a low pass filter (C5229,L5225,and C5226) which attenuates harmonics and provides correct 
level to close the synthesizer loop.
The pre-scaler in the synthesizer (U5201) is a dual modulus pre-scaler with selectable divider ratios. 
The divider ratio of the pre-scaler is controlled by the loop divider, which in turn receives its inputs via 
the SRL. The output of the pre-scaler is applied to the loop divider. The output of the loop divider is 
connected to the phase detector, which compares the loop divider´s output signal with the reference 
signal.The reference signal is generated by dividing down the signal of the reference oscillator 
(Y5261 or Y5262).
The output signal of the phase detector is a pulsed dc signal routed to the charge pump. The charge 
pump outputs a current at U5201, pin 43 (IOUT). The loop filter (consisting of R5221-R5223, C5221-
C5225, and L5221) transforms this current into a voltage that is applied to varactor diodes CR5311 
for transmit, CR5301, CR5302 and CR5303 for receive and alters the output frequency of the 
VCO.The current can be set to a value fixed in the LVFRAC-N IC or to a value determined by the 
currents flowing into BIAS 1 (U5201-40) or BIAS 2 (U5201-39). The currents are set by the value of 
R5251 or R5252 respectively. The selection of the three different bias sources is done by software 
programming.
To reduce synthesizer lock time, when new frequency data has been loaded into the synthesizer, the 
magnitude of the loop current is increased by enabling the IADAPT (U5201-45) for a certain software 
programmable time (Adapt Mode). The adapt mode timer is started by a low to high transistion of the 
CSX line. When the synthesizer is within the lock range, the current is determined only by the 
resistors connected to BIAS 1, BIAS 2, or the internal current source. A settled synthesizer loop is 
indicated by a high level of signal LOCK (U5201-4) which is routed to one of the µP´s ADCs input 
U101-56. From the voltage the µP determines whether LOCK is active.
To modulate the PLL, the two-spot modulation method is utilized via pin 10 (MODIN) on U5201. The 
audio signal is applied to both the A/D converter (low frequency path) and the balanced attenuator 
(high frequency path). The A/D converter converts the low frequency analog modulating signal into 
a digital code which is applied to the loop divider, thereby causing the carrier to deviate. The 
balance attenuator is used to adjust the VCO’s deviation sensitivity to high frequency modulating 
signals. The output of the balance attenuator is present at the MODOUT port (U5201-41) and 
connected to the VCO modulation diode CR5321 via R5321 and C5325. 
						

							2-10Frequency Synthesis
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							3-1
Section 3
TROUBLESHOOTING CHARTS
1.0 Troubleshooting Flow Chart for Receiver (Sheet 1 of 2)
Bad SINAD
Bad 20dB Quieting
No Recovered AudioSTART
Audio at 
pin 8 of 
U3101 ?Check Controller
(in the case of no audio)
OR ELSE go to “B” Ye s
No
Spray or inject 44.85MHz 
into XTAL Filter FL3101
Audio heard ?BYe s
No
Check 2nd LO 
(44.395MHz) at C3135 
LO present ?BYe s
 Check voltages on 
U3101Biasing OK ?
No
No
A
Ye s
Check Q3102  bias 
for faults
Replace Q3102
Go to B
Ye s
No
Check circuitry 
around U3101.
Replace 
U3101 if defect
Check circuitry around Y3101. 
Replace Y3101 if defectVoltages
 OK? 
						

							3-2Troubleshooting Flow Chart for Receiver
1.1Troubleshooting Flow Chart for Receiver (Sheet 2 of 2)
IF Signal at 
C3101?
No
RF 
Signal at 
T5051?
RF
Signal at 
C5015?
No
No
RF
Signal at 
C5025?
No or 
Check harmonic filter
L5491-L5493, C5492, J5401
and ant. switch
D5471, D5472, L5472.
Check filter between 
C5025 & C5009. 
Check tuning voltage 
at R5060.
Inject RF into J5401
Is
tuning voltage
OK?
No
Ye s
Check RF amp (Q5003) 
Stage.
Check filter between 
C5015 & T5051.
Ye s
Check T5051, T5052, 
D5051, R5052, L5008.
Ye s
1st LO level 
OK?
Locked?Ye s
Check FGU
Ye s
Trace IF signal 
from C3101 to 
Q3101. Check for 
bad XTAL filter.
No
Ye sIF
signal at Q3102 
collector?
Before replacing 
U3101, check 
U3101 voltages.
Ye s
Check for 
5VDC
Is 9V3 
present?
Check Supply Voltage 
circuitry. Check Q0681, 
U5211 and U0641.
No
No
No
Check U5501. 
Check varactor filter.
NoYe s
Ye s
Ye s
A
A
B
weak RFRF
Signal at 
C5009? 
						

							Troubleshooting Flow Chart for 40W Transmitter 3-3
2.0 Troubleshooting Flow Chart for 40W Transmitter 
No
Is Q5441 OK ?
Ye s
Is drive from VCO
        >+4dBm? NoIs voltage drop across
     R5497 >4.5V ?No
Check Q5431 gate(open)
and drain resistances
            (11kohm)NoCheck Q5421 gate(open)
and drain resistances
             (11kohm)No
PCIC_MOSBIAS_1        Check
No
No
Change
Q4573 
              START
        No power
  
  Is Vctrl
there? Is Q5573
   OK?
Check voltage
n U5501, pin 4 
Check voltage
on U5501, pin 5
Check R5422-5
and go back to top
Troubleshoot
ASFIC
Change
PCIC
Check R5409 and
 R5473 and go back
to top
     CheckMOSBIAS_2Check
ASFIC
Are D5471 &
D5472 OK?Change
D5471 &
D5472
No NoNo
Ye sYe sYe s Ye s Ye sYe s
Ye s Ye s
No
NoCheck
PCIC
Ye s
Change Q5421
Change Q5431
Ye s
Change U5401
Ye sDo visual check
on all components
No
Change Q5441
Troubleshoot
        VCO
Check voltage
on TP5531 
						

							3-4Troubleshooting Flow Chart for Synthesizer
3.0 Troubleshooting Flow Chart for Synthesizer
5V
 at pin 6 of 
D5201
Is
information
from
 µP U0101
correct
?
Is
U5201 Pin 47
at = 13VDC
?
Is
U5301 Pin 19
4.5 VDC in TX?  
(at VCO section)
?
Sta rt
Visual 
check of the 
Board
OK?Correct
Problem
Check 5V
Regulator
U5211
+5V
at U5201
Pins
13 & 30
?
Is
16.8MHz
Signal at U5201 
Pin 19
?
Check
Y5261 / Y5262 and 
associated parts
Are
signals
at Pins 14 &15 
of U5201
?
Check 
R5201Check C5381
Is
U5201
Pin 2  >4.5 VDC in 
Tx & 
						

							Troubleshooting Flow Chart for VCO3-5
4.0 Troubleshooting Flow Chart for VCO
Are Q5332
Base at 0.7V 
Collector at 4.5V 
Emitter at 110mV
Are Q5301
Base at 2.4V 
Collector at 4.5V 
Emitter at 1.7VAre Q5311 
Base = 1.9V
Collector = 4.5V
Emitter = 1.3V
Low or no RF Signal
at TP5003
Visual check
of board
OK?
35mV DC at
U5301 Pin 19
NO
YES
Replace Q5301
at base of Q5332
NO
NO
NO
NO YES
YES
YESYESLow or no RF Signal
at input to PA
4.8V DC at
U5301 Pin 19
Is RF available 
at U5401
YES
YESYES YES NO
NO
NO
NO
NO
Audio =180mVrmsat “-” Side of 
4.5VDC
at CR5321
If C5321 and R5321 are OK,
 then replace CR5321
Replace C5322
Replace C5325
NONO
YES
YES
 
TX VCO
RX VCO
Correct
ProblemVisual check
of board
OK?
Check runner 
between U5201 Pin 2 
and U5301 Pin 19
Is RF available 
If all parts from U5301 Pin 8
to Base of Q5332 are OK, 
replace U5301
If all parts associated 
with the pins are OK, 
replace Q5332
If all parts from collector
of Q5332 to TP5003 are
OK, Replace U5301
Power OK but 
no modulation
If all parts from U5301 Pin 10
U5401 Pin 16 are OK,
replace U5301
Replace 
Q5311
YESYES
Make sure Synthesizer is 
working correctly and runner 
between U5201 Pin 28 and 
U5301 Pin 14 & 18 are OK 4.5V DC 
OK ?
OK?
OK?
C5325  at U5301 Pin 14 & 18    4.5V DC 
OK ? at U5301 Pin 14 &18    
NO
Pin 16
If R5361 and 
L5361 are OK, 
replace U5301 
						

							3-6Troubleshooting Flow Chart for VCO
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							4-1
Section 4
UHF PCB/SCHEMATICS/PARTS LISTS
1.0 Allocation of Schematics and Circuit Boards
1.1 Controller Circuits
The UHF circuits are contained on the Printed Circuit Board (PCB) which also contains the 
Controller circuits. This Chapter shows the schematics for the UHF circuits only, refer to the 
Controller section for details of the related Controller circuits . The PCB component layouts and the 
Parts Lists in this Chapter show both the Controller and UHF circuit components. The UHF 
schematics and the related PCB and parts list are shown in the tables below.
Table 4-1   UHF B2 40W Diagrams and Parts Lists
PCB :
8480645Z04 Main Board Top Side
8480645Z04 Main Board Bottom SidePage 4-3
Page 4-4
SCHEMATICS
Power Amplifier 40W
FRACN
Voltage Controlled Oscillator
Receiver Front End
IF
Page 4-5
Page 4-6
Page 4-7
Page 4-8
Page 4-9
Parts List
8480645Z04 Page 4-10 
						

							4-2Allocation of Schematics and Circuit Boards
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